One type of such crane has a counterweight which is mounted on a beam assembly at the rear end of the crane jib superstructure. The beam assembly and counterweight is movable out from or towards the superstructure by the use of hydraulic rams or the like to balance the jib under varying loads.
When such a crane is to be driven along a road, the jib is folded down over the deck or platform of the vehicle and secured thereto and it is desirable for the counterweight to be removed from the superstructure and secured to the vehicle, not at one end, but rather in a position where its weight can better be carried by the vehicle suspension. Hitherto, in order to remove the counterweight from the beam, it has been necessary first to contract the beam towards the crane superstructure. Then, by using a vertically acting hydraulic ram to support the counterweight whilst it is unbolted from the beam and finally using the "vertical" hydraulic ram, to lower the counterweight to the deck of the vehicle where it is secured for travel.
This previously proposed system requires two degrees of movement and hence two rams or sets of rams, namely an "in" movement of the beam and a "down" movement of the counterweight. Similarly for reattachment, the counterweight has had to be lifted up and secured to the beam and the beam then moved in towards the jib superstructure.
It is therefore an object of the invention to simplify the removal and reattachment of the counterweight whilst still allowing the counterweight to be fixed to a desired position on the vehicle.